1. Field of the Invention
The present invention relates to a magnetic disk that utilizes a thermally assisted method during magnetic recording in a magnetic recording apparatus.
2. Description of the Related Art
As a digital information technology develops, high capacity of a recording apparatus and miniaturization and light weight of an apparatus are in demand. In order to respond to the demand, in a magnetic recording apparatus, in particular, a magnetic disk recording apparatus (for example, Hard Disk Drive (HDD)), a high recording density is being pursued. In recent years, developments and researches for achieving a surface recording density of 1 Tb/in2 or more are under way.
The high recording densification of a magnetic disk recording apparatus has been realized by miniaturizing a dimension of a recording bit. However, as the recording bit is miniaturized, there occurs a problem that a thermal fluctuation phenomenon where the magnetization is destabilized owing to thermal energy remarkably appears and thereby recorded information is lost. In order that the recorded information is recorded for a practical period, it is required to increase a volume of a magnetic particle constituting the recording bit that is the minimum unit of information in an information recording medium or to increase its coercive force. When the miniaturization is forwarded, since there is a limit to increase a volume of the magnetic particle, it becomes necessary to increase the coercive force of the magnetic particle.
However, when the coercive force of a magnetic body is immoderately increased, a recording medium is not sufficiently magnetized and is incapable of effecting saturation recording in writing information under a magnetic field generated by a magnetic head; accordingly, there occurs a problem that the over-write characteristics are deteriorated, which is a fatal problem for the magnetic recording medium.
In order to solve the problem, a thermally assisted recording method has been proposed as a countermeasure during the magnetic recording.
The thermally assisted recording method is a recording method where a magnetic body that is a recording medium is locally heated during writing-in of information to lower the coercive force to magnetize the magnetic body by a magnetic field of a magnetic head to record. As a method of heating a magnetic body that is a recording medium, a thermally assisted magnetic recording head where the recording medium is heated by illuminating with laser light has been disclosed (for example, Japanese Patent Application Laid-Open No. 2002-117502). According to the thermally assisted recording method, a bit recording density per one track (circumferential direction) (Bit Per Inch: BPI) is increased to increase the surface recording density.
On the other hand, in a discrete track medium, a non-recording region that magnetically separates is disposed between adjacent magnetic recording regions for recording to inhibit the adjacent magnetic recording portions from interfering with each other. Thereby, a track density (TPI) in a radial direction can be increased. Furthermore, as a medium analogous to a discrete track medium (DTM) where a magnetic recording region and a non-recording region are disposed in parallel in track, there is a bit patterned medium (BPM) obtained by, while a magnetic recording region and a non-recording region are adjacently disposed, artificially and regularly disposing a non-recording region also between the recording bits (for example, Japanese Patent Application Laid-Open No. 2008-226428).
The surface recording density of a magnetic disk is determined by a product of the BPI and the TPI.